Overlay Measurement Apparatus Using Partial Area Segmentation
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Solution Overview
Problem
The increasing demand for accurate overlay measurement in image-based overlay measurement systems, particularly in lithographic processes, is hindered by the influence of optical aberrations such as coma aberration, which can lead to errors when measuring small marks on reticles, limiting the number of marks that can be placed on a scribe line and affecting measurement accuracy.
Innovation Solution
An overlay/alignment measurement method and apparatus that involves preliminary measurement of overlay shift by shifting a measurement area relative to the mark, dividing the measurement area into partial areas, calculating tool-induced shifts and repeatability, and determining the optimal partial area to minimize aberration effects, allowing for precise alignment even with smaller marks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of the mark for overlay measurement is reduced to increase the number of marks on the scribe line, then the number of marks increases, but the lens aberration of the optical microscope influences the accuracy of overlay measurement
Solution Approach 1:
The measurement area is divided into multiple partial areas, and overlay measurement is performed separately in each partial area. This segmentation allows the system to handle small marks more effectively by measuring them in isolated regions, reducing the impact of optical aberrations that affect the entire field of view.
Solution Approach 2:
The invention applies different measurement strategies to different partial areas based on local optical conditions. By evaluating tool-induced shifts and repeatability in each partial area, the system identifies and selects the partial area with the best measurement quality, ensuring accurate overlay measurement even when marks are small and numerous.
2Measurement precision
If the number of sampling points is increased to perform accurate overlay measurement, then the accuracy of overlay measurement improves, but the complexity of the measurement system increases
Solution Approach 1:
The measurement area is divided into multiple partial areas, allowing the system to perform measurements in smaller, more manageable regions. This segmentation enables accurate overlay measurement with appropriate sampling points in each region without requiring excessive complexity across the entire measurement system.
Solution Approach 2:
The system dynamically evaluates parameters such as tool-induced shift and repeatability in each partial area, and selects the optimal partial area for measurement based on these parameters. This adaptive approach allows the system to maintain high measurement accuracy while adjusting the complexity of the measurement process to the specific requirements of each partial area.
3Quantity of substance
If the mark size is reduced to accommodate more marks on the scribe line, then more marks can be disposed on the scribe line, but the optical image of the mark shifts due to comatic aberration
Solution Approach 1:
By dividing the measurement area into multiple partial areas, the system can measure small marks in isolated regions where optical aberrations have less cumulative effect. This segmentation helps maintain the stability of the optical image position even when marks are reduced in size to increase their number on the scribe line.
Solution Approach 2:
The system evaluates the local optical quality in each partial area by measuring tool-induced shifts and repeatability. It then selects the partial area with the best optical quality for measurement, ensuring that marks are measured in regions where comatic aberration and other optical aberrations have minimal impact on image position stability.
Data Source
AI summary
According to one embodiment, a method includes preliminarily measuring the amount of overlay or alignment shift of the mark for overlay or alignment measurement while sequentially shifting a position of a measurement area relative to the mark for overlay or alignment measurement so as to position the mark for overlay or alignment measurement on each of a plurality of partial areas. The measurement area corresponds to a field angle of the optical measurement system, and an inside of the measurement area is two-dimensionally divided into the partial areas. The method includes calculating a tool-induced shift regarding a characteristic deviation of the optical measurement system for each of the plurality of partial areas based on a preliminarily measured result of the amount of overlay or alignment shift. The method includes determining a partial area to be used from among the plurality of partial areas on the basis of the tool-induced shift calculated for each of the plurality of partial areas.